The present invention relates to electronic throttle control devices and in particular to an electronic sensor for indicating pedal position to an electronic throttle controller.
Electronic controls and computers are well known in the art of automotive manufacturing. It is not unusual for a late model automobile to have a computer for monitoring and controlling many of its operating systems. Typically an input stage may include data collection by sensors. The collected data is input to a processing stage where an electronic control module interprets the data and calculates appropriate output for delivery to an output stage. Actuators within the output stage convert the appropriate output to a desired physical movement. One such operating system includes the electronic throttle control (ETC). In the ETC system, often referred to as a xe2x80x9cdrive-by-wirexe2x80x9d system, the accelerator pedal is not connected to the throttle body by a cable, as in earlier model vehicles, but rather by an electrical connection between the pedal and a throttle controller, as described by way of example in U.S. Pat. Nos. 5,524,589 and 6,073,610. As described by way of example with reference to U.S. Pat. No. 6,098,971, a potentiometer typically replaces the cable that normally runs to the throttle body and electrical wires send pedal position information to a computer. As a result, the pedal must now have its own springs. With each spring having its own feel and not a hysteresis effect as does a cable in a sheath, a spring and mechanical hysteresis device is provided for operation with the pedal for simulating the feel of a traditional early model cable styled accelerator pedal. A pedal position sensor provides an electrical voltage output responsive to pedal angular position. The pedal position sensor typically includes a resistive potentiometer having two or more resistive tracks for redundancy in providing an output signal indicative of the pedal position. Output signal faults are detected through correlation measurements between the output signals from each of the tracks. Typically, it is necessary to maintain a close tolerance on the idle and wide-open throttle output voltage signal and on stability of these signals over time.
There is a need in the industry, when using ETC pedal assemblies, to provide a way by which the idle output voltage set points are maintained despite the buildup of assembly tolerances for parts within the assembly. The set points built into the pedal and sensor assembly typically control the engine idle speed and must be maintained to a relatively tight tolerance. Two typical tolerance band specifications have emerged: either +/xe2x88x923.5% or +/xe2x88x921% of the reference voltage (Vref) applied to the sensor potentiometer. It would be desirable to achieve a net build condition that meets this tolerance requirement. It would further be desirable to achieve a condition in which parts could be assembled to have a net build condition that falls within the appropriate tolerance band without the need for final assembly adjustment.
By way of example, a complicating factor in pedal position sensor assemblies is the fact that total angular travel of the sensor is relatively small, typically in the range of a 15 degree arc to a 20 degree arc. Therefore, any errors in reference angles represent a significant portion of the total sensor output. Conversely, even generous tolerances on sensor output voltage, equate to extremely tight control of sensor and pedal assembly physical dimensions. For example, and idle set-point tolerance of +/xe2x88x921% Vref is only a +/xe2x88x920.25 degree rotation of the drive shaft. There exists a need to quickly and easily calibrate a final ETC pedal assembly while maintaining an accurate and stable adjustment process. There is further a need for a position sensor which can be effectively and economically integrated with the pedal assembly without introducing a packaging problem for vehicles manufacturers while providing a robust structure able to meet the environmental conditions generally demanded.
In view of the foregoing background, it is therefore an object of the present invention to provide a pedal operable with an electronic throttle controller that can be easily and effectively calibrated and adjusted during assembly of the pedal. It is further an object of the present invention to provide a reliable yet inexpensive pedal position sensor that accurately represents pedal position.
These and other objects, advantages and features of the present invention are provided by a position sensor useful with an electronic throttle control pedal wherein the sensor comprises a potentiometer having a slider member slidable with a substrate in only a linear direction for providing an electrical output representative of a linear displacement of the slider member along the linear direction, and a drive arm rotated by a pedal shaft and operable with the slider member for providing the linear displacement to the slide member through a rotational movement of the shaft and thus the drive member. The drive arm includes a first arm member operable with a second arm member for providing a telescoping longitudinal length adjustment to the drive arm during calibration of the sensor. With a desired calibration setting of the potentiometer, the first arm member is locked to the second arm member at a fixed position along a drive arm longitudinal axis which extends radially from an axis of rotation of the pedal shaft. A slot in the first arm members has a slot longitudinal axis at a non-zero angle to the drive arm longitudinal axis with the slider member adapted for slidable movement along the slot longitudinal axis.
A method aspect of the present invention includes assembling a position sensor with an electronic throttle control pedal, wherein the pedal is operable for rotating a shaft carried by a bracket. The method comprises providing a potentiometer having a substrate and a slider member slidably connected to the substrate for movement along only a linear direction to provide an electrical output signal indicating a linear displacement of the slider member along the substrate. A drive arm having telescoping first and second arm members is adjustable along a longitudinal axis of the drive arm for fixing the drive arm at a preselected length, the first arm member having a slot for slidably receiving a coupler. The method includes connecting the second arm member to the shaft for rotation of the second arm member by the shaft responsive to movement of the pedal. During assembly, the first arm member is slid onto the second arm member in a telescoping arrangement along the longitudinal axis of the drive member. A coupler is rotatably attached to the slider member and guided into the slot. The slider member is biased toward an initial position on the substrate. The coupler then engages the slider member for moving the slider member from the initial position into an active measuring position. Measurements of the electrical signals from the potentiometer are made while continuing to slide the first arm member onto the second arm member for achieving a desired electrical signal output. Once the desired output is achieved, the first arm member is affixed to the second arm member for operation of the sensor in determining a pedal position. In one method, the initial position is below an idle position, and the desired electrical signal provides the idle position for an accelerator pedal.